Multimedia conference calls typically involve communicating voice, video, and/or data information between multiple endpoints. With the proliferation of data networks, multimedia conferencing is migrating from traditional circuit-switched networks to packet networks. To establish a multimedia conference call over a packet network, a conferencing server typically operates to coordinate and manage the conference call. The conferencing server receives a video stream from a sending participant and multicasts the video stream to other participants in the conference call.
One problem associated with communicating multimedia information such as digital video for a video conference call is that digital video (sometimes combined with embedded digital audio) often consumes large amounts of storage and transmission capacity. A typical raw digital video sequence includes 15, 30 or even 60 frames per second (frame/s). Each frame can include hundreds of thousands of pixels. Each pixel or pel represents a tiny element of the picture. In raw form, a computer commonly represents a pixel with 24 bits, for example. Thus a bit rate or number of bits per second of a typical raw digital video sequence can be on the order of 5 million bits per second (bit/s) or more. Most media processing devices and communication networks lack the resources to process raw digital video. For this reason, media communication systems use source compression (also called coding or encoding) to reduce the bit rate of digital video. Decompression (or decoding) reverses compression.
Typically there are design tradeoffs in selecting a particular type of video compression for a given processing device and/or communication network. For example, compression can be lossless where the quality of the video remains high at the cost of a higher bit rate, or lossy where the quality of the video suffers but decreases in bit rate are more dramatic. Most system designs make some compromises between quality and bit rate based on a given set of design constraints and performance requirements. Consequently, a given video compression technique is typically not suitable for different types of media processing devices and/or communication networks. This may be particularly problematic when one or more receiving devices utilize multiple display frames, windows or other objects to display video information for different participants in a multimedia conference call. This is further exacerbated when different participants appear in different display windows to accommodate different sets of speakers.